Suspension apparatus of a vehicle

ABSTRACT

A suspension apparatus of a vehicle has a cylinder unit interposed between a sprang weight and an unsprung weight, which changes a ride height of the vehicle body by supplying or discharging an operating liquid through a supply/discharge control valve. The supply/discharge control value is controlled on the basis of a predetermined condition so as to control a posture of the vehicle body. There are further provided a rebound detecting sensor for detecting a rebound of each of the wheels, which occurs further from a state in which the wheel is rebounded, and a pressure detecting sensor for detecting a pressure in the cylinder unit. When it is sensed by the rebound detecting sensor that the rebound occurs further from the rebounding state, if the pressure detected by the pressure detecting sensor is continued in an elevating state for a given period of time, it is judged that the supply/discharge control valve is in trouble.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a suspension apparatus of a vehicleadapted to change suspension characteristics.

2. Description of Related Art

Recently, as a suspension apparatus of a vehicle is called an activesuspension, it is proposed that the suspension apparatus is of a type inwhich its suspension characteristics can be changed in an arbitrarymanner. The so-called active suspension is basically constructed suchthat a cylinder unit is interposed between an unsprung weight and asprang weight and that the suspension characteristics are controlled bycontrolling a supply and discharge of operating liquid to and from thecylinder unit. Japanese Patent Publication (Kokoku) No. 14,365/1984discloses a suspension apparatus which uses a cylinder unit as anactuator for adjusting a ride height of the vehicle body and whichcontrols a posture of the body by controlling a pressure of theoperating liquid in the cylinder unit.

In the so-called active suspension, suspension characteristics canlargely be changed by supplying the operating liquid or discharging itto or from outside in order to carry out various control includingcontrol of the ride height of the vehicle body, control of a rollcomponent of vibration of the body, control of a pitch component ofvibration thereof, and so on.

In the active suspension, there has generally been used a ride heightsensor for sensing the ride height of the vehicle body for control ofthe posture of the vehicle body so that the suspension control cannot beimplemanted to a sufficient extent if the ride height sensor would be introuble. Japanese Patent Unexamined Publication (kokai) No 289,417/1987proposes that whether the ride height sensor is in trouble or not isjudged by observing a velocity of changes in output values from the rideheight sensor. Japanese Patent Unexamined Publication (kokai) No.282,110/1986 proposes that a portion of plural ride height sensors isjudged to be in trouble when output from the portion of the plural rideheight sensors does not vary although outputs from the plural rideheight sensors are actually varying.

It is thus to be noted that the active control of the suspension isimpaired when a supply/discharge control valve for supplying ordischarging the operating liquid to or from the cylinder unit is out oforder, particularly when the supply/discharge control valve is fixed insuch a state that the operating liquid is being supplied.

SUMMARY OF THE INVENTION

Therefore, the present invention has the object to provide a suspensionapparatus of a vehicle capable of accurately sensing a state in whichthe supply/discharge control valve is in trouble in such a state that itis supplying the operating liquid.

In order to achieve the foregoing object, as diagrammatically shown inFIG. 13, the present invention consists of a suspension apparatuscomprising:

a cylinder unit interposed between a sprang weight and an unsprungweight for changing a ride height by supplying or discharging anoperating liquid;

a supply/discharge control valve for supplying to or discharging fromthe cylinder unit;

a supply/discharge control means for controlling supply of the operatingliquid to or discharge of the operating liquid from the cylinder unit bycontrolling the supply/discharge control valve on the basis of apredetermined condition;

a rebound detecting means for detecting a rebound of a wheel, whichfurther occurs when the wheel is rebounding;

a pressure detecting means for detecting a pressure in the cylinderunit; and

a trouble judging means for judging a trouble of the supply/dischargecontrol valve when the pressure detected by the pressure detecting meansis continued in an elevating state for a given period of time when therebound is detected by the rebound detecting means.

It can be anticipated that the pressure in the cylinder unit be loweredwhen the wheels are rebounded and, if the pressure would be elevated,this is caused by the fact that the operating liquid is kept suppliedand the supply control valve is in trouble. With attention paidbasically to this point, in order to improve an extent of the troublejudgment, there are added thereto conditions that the vehicle body befurther rebounded from a rebounded state and that the pressure in thecylinder unit is elevating be continued for a given period of time.

Other objects, features and advantages of the present invention willbecome apparent in the course of the description of the preferredembodiments which follows, with reference to the accompanying drawings

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation showing an operating liquid circuitaccording to one example of the present invention.

FIG. 2 is a sectional view showing one example of a pilot valve.

FIG. 3 represents a control system of the circuit of FIG. 1, togetherwith an example of disposition of vertical acceleration sensors.

FIG. 4 is a perspective view showing another example of disposition ofthe vertical acceleration sensors.

FIG. 5 is a sectional view showing one example of the accelerationsensor.

FIGS. 6-8 each represent a control system showing one example forcarrying out active control.

FIG. 9 represents an example of roll characteristic in the vehicle of anactive suspension type.

FIG. 10 represents an example of roll characteristic in the vehicle of apassive suspension type.

FIGS. 11 and 12 each are a flow chart showing a control example of thepresent invention.

FIG. 13 is a block diagram showing a whole construction of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described more in detail by way ofexamples with reference to the accompanying drawings.

In the following description and the accompanying drawings, referencesymbol "F" stands for a front wheel and "R" stands for a rear wheel, aswell as reference symbol "FR" stands for a right-hand front wheel, "FL"for a left-hand front wheel, "RR" for a right-hand rear wheel, and "RL"for a left-hand rear wheel. When the front and rear wheels as well asthe right-hand and left-hand wheels are not needed to be distinguished,reference numerals are referred to without using these referencesymbols.

Operating Liquid Circuit

As shown in FIG. 1, reference numeral 1 denotes a cylinder unit which ismounted to each of the wheels, a cylinder unit mounted to the right-handfront wheel being referred to as 1FR, a cylinder unit mounted to theleft-hand front wheel as 1FL, a cylinder unit mounted to the right-handrear wheel as 1RR, and a cylinder unit mounted to the left-hand rearwheel as 1RL. Each of these cylinder units comprises a cylinder 2connected to the unsprung weight and a piston rod 3 extending from theinside of the cylinder 2 and connected to a sprang weight. The cylinder2 comprises the piston rod 3, a piston 4 integral with the piston rod 3,a liquid chamber 5 disposed upward and defined by the piston 4 and alower chamber disposed downward of the liquid chamber 5 and communicatedtherewith. This structure allows the piston rod 3 to extend raising aride height of the vehicle body when an operating liquid is fed to theliquid chamber 5 while lowering the height of the vehicle body when theoperating liquid is discharged from the liquid chamber 5.

To the liquid chamber 5 of each cylinder unit 1 is connected a gasspring 6 (6FR, 6FL, 6RR, and 6RL) which comprises four cylindricalsprings 7 of a small diameter and the four cylindrical springs 7 arearranged in a row, or in parallel to each other, and connected to theliquid chamber 5 through orifices 8. Three of the four cylindricalsprings 7 are further connected to the liquid chamber 5 through a shiftvalve 9. This arrangement enables the four cylindrical springs 7 to becommunicated with each other only through the orifices 8 when the shiftvalve 9 is located at a shift position as shown in the drawing, therebymaking a damping force smaller at this time. When the shift valve 9 isshifted from the position as shown in the drawing, the three cylindricalsprings 7 can be communicated with each other through an orifice 10incorporated in the shift valve 9, too, thereby making a damping forcelarger. It is to be noted as a matter of course that a displacement ofthe shift positions of the shift valve 9 changes spring characteristicsof the gas spring 6. Furthermore, it is to be noted that suspensioncharacteristics can also be changed by an amount of the operating liquidto be fed to the liquid chamber 5 of the cylinder unit 1.

Referring to FIG. 1, reference numeral 11 denotes a pump to be driven bythe engine, and the pump 11 raises a high-pressure operating liquid froma reservoir tank 12 and discharges the liquid into a common passage 13as a supply passage. The common passage 13 is branched into a forwardpassage 14F and a rearward passage 14R, the forward passage 14F beingfurther branched into a right-hand forward passage 14FR and a left-handforward passage 14FL. The right-hand forward passage 14FR is connectedto the liquid chamber 5 for the right-hand front wheel cylinder unit 1FRand the left-hand forward passage 14FL is connected to the liquidchamber 5 of the left-hand front wheel cylinder unit 1FL. To theright-hand forward passage 14FR are connected on the upstream side aflow rate control valve 15FR for supplying the operating liquid and onthe downstream side a pilot valve 16FR as a delay valve. To theleft-hand forward passage 14FL are connected on the upstream side a flowamount control valve 15FL for supplying and on the downstream side apilot valve 16FL.

To the right-hand forward passage 14FR is connected a first reliefpassage 17FR for the right-hand forward passage at a position betweenthe supply flow rate control valves 15FR and 15FL, and the first reliefpassage 17FR leads eventually to a reservoir tank 12 through a reliefpassage 18F for the front wheels. To the first relief passage 17FR isconnected a discharge flow amount control valve 19FR. The right-handforward passage 14FR disposed on the downstream side of the pilot valve16FR is connected through a second relief passage 20FR as a bypassbypassing the discharging flow amount control valve 19FR to the firstrelief passage 17FR which is connected to a relief valve 21FR. Theright-hand forward passage 14FR is provided with a filter 29FR at aposition close to the cylinder unit 1FR. The filter 29FR is disposed ata position among the cylinder unit 1FR, the pilot valve 16FR disposedcloser to the cylinder unit 1FR, and the relief valve 21FR, functioningas preventing dust abraded or worn off as a result of abrasion and so onfrom flowing toward the pilot valve 16FR and the relief valve 21FR.

It is to be noted that the arrangement for passages for the left-handforward wheel is substantially the same as that for the right-handforward wheel as have been described hereinabove, so that a duplicatedescription thereon will be omitted herefrom for a brevity ofexplanation.

To the common passage 13 is connected a main accumulator 22, and to thefront-wheel relief passage 18F is connected an accumulator 23F. The mainaccumulator 22 serves as a source of accumulating pressures for anoperating liquid in association with a sub-accumulator 24, as will bedescribed hereinafter, and it functions as preventing an amount of theoperating liquid to be supplied to the cylinder unit 1 from runningshort. The accumulator 23F prevents a high-pressure operating liquid inthe cylinder units 1 for the front wheels from being discharged rapidlyto the reservoir tank 12 of a low pressure, namely, prevents a so-calledwater-hammer phenomenon.

Passages for supplying or discharging the operating liquid to or fromthe cylinder units 1RR and 1RL for the rear wheels are constructed in away similar to those for the front wheels so that a duplicatedescription will be omitted from the description which follows. It is tobe noted, however, that the passages for the rear wheels are providedwith no valves corresponding to the relief valves 21FR and 21FL for therespective cylinder units 1FR and 1FL and that the rear-wheel passage14R is provided with the sub-accumulator 24 with the fact taken intoaccount that a length of its rear-wheel passage from the mainaccumulator 22 becomes longer than that of the front-wheel passage.

The common passage 13, namely, each of the front-wheel passage 14F andthe rear-wheel passage 14R, is connected to the front-wheel reliefpassage 18F through a relief passage 25 to which, in turn, is connecteda safety valve 26 consisting of an electromagnetic switch valve.

In FIG. 1, reference numeral 27 stands for a filter and referencenumeral 28 for a pressure governing valve for adjusting a dischargepressure from the pump 11 so as to be within a given range. In thisembodiment, the pressure governing valve 28 is constituted such that thepump 11 is of a variable-displacement, swash plate type piston that isintegrally incorporated into the pump 11. The pressure governing valve28 can adjust the discharge pressure within the range from 120 to 160kg/cm².

The pilot valve 16 is arranged so as to be shifted to open or close inaccordance with a differential pressure between the pressures of thefront-wheel passage 14F or the rear-wheel passage 14R, namely, betweenthe pressure in the common passage 13 and that on the side of thecylinder unit 1. At this end, the front-wheel 14F is led to thefront-wheel common pilot passage 31F which, in turn, is branched intotwo branch passages 31FR and 31FL, and the right-hand front wheel branchpassage 31FR is connected to the right-hand pilot valve 16FR while theleft-hand branch passage 31FL is connected to the left-hand pilot valve16FL. The common pilot passage 31F is provided with an orifice 32F. Apilot passage for the rear wheels is arranged like the pilot passage 31Ffor the front wheels.

Each of the pilot valves 16 may be constructed as shown in FIG. 2. Thepilot valve 16 as shown in FIG. 2 is directed to one for the right-handfront wheel, which is provided in a casing 33 with a main flow passage34 constituting part of the right-hand forward passage 14FR to which themain flow passage 34 is connected. A valve seat 35 is provided in anintermediate position of the main flow passage 34 on or from which aswitching piston 36 is seated or separated so as to close or open thepiston valve 16FR, the switching piston 36 being slidably inserted intothe casing 33.

The switching piston 36 is formed integrally with a control piston 38through a valve stem 37. The control piston 38 is slidably inserted inthe casing 33 and defines a liquid chamber 39 in the casing 33. Theliquid chamber 39 is then connected to the branch pilot passage 31FRthrough a control flow passage 40. The control piston 36 is urged by areturn spring 41 in the direction in which the switching piston 36 isbeing seated on the valve seat 35, in other words, in which the pilotvalve 16FR is closed. Furthermore, the control piston 38 is designedsuch that a pressure of the main flow passage 34 acts upon the controlpiston 36 through a communication hole 42 on the side opposite to theliquid chamber 39. This arrangement allows the switching piston 36 to beseated on the valve seat 35 to close the pilot valve 16FR as thepressure in the liquid chamber 39 on the side of the common passage 13has declined to one quarter or less than the pressure in the main flowpassage 34 on the side of the cylinder unit 1FR. In this case, when thepressure on the side of the common passage 13 declines to a large extentfrom a state in which the pilot valve 16FR is open, this decline in thepressure is delayed by means of an action of the orifice 32F and thentransmitted to the liquid chamber 39 whereby a closure of the pilotvalve 16FR is delayed after the decline in the pressure. It is to beprovided that this delay time is set to approximately one second in thisembodiment.

Actions of all the valves will be described in more detail hereinafter.

(1) Shift Valve 9

The shift valve 9 is shifted to make a damping force greater only duringcornering in this embodiment.

(2) Relief Valve 21

The relief valve 21 is closed under ordinary conditions and opened asthe pressure on the side of the cylinder unit 1 reaches a given value orhigher. In this embodiment, the given value is set to 160 to 200 kg/cm².In other words, this valve serves as a safety valve for preventing anabnormal rise in the pressure on the side of the cylinder unit 1.

It is noted that the relief valve 21 may be mounted to the cylinderunits 1RR and 1RL for the rear wheels, however, in this embodiment, therelief valve 21 can be mounted on the rear wheels with the fact takeninto account that the vehicle body is designed such that the pressure onthe side of the rear wheels does not become larger than that on the sideof the front wheels on condition that the weight on the front side ofthe vehicle body is allotted considerably heavier than that on the rearside thereof.

(3) Flow Amount Control Valves 15 and 19

The supply amount rate control valve 15 and the discharge flow amountcontrol valve 19 each are spool valves of electromagnetic type andswitched from a closed state to an open state or vice versa. It isprovided, however, that there is provided a pressure-differentialcontrol mechanism so as to make a difference between the pressure on theupstream side and that on the downstream side substantially constantwhen they are in an open state, because a constant pressure differentialis required for control over a flow amount. More specifically, the flowamount control valves 15 and 19 are designed so as to vary with theirpositions, i.e., with their opening angles, in which their spoolsdisplace in proportion to the current to be supplied. The current to besupplied is determined on the basis of a map in advance prepared andstored, which represents the relationship of the flow amount with thecurrent. In other words, the current is supplied in correspondence witha flow amount required at that time.

The flow amount control valves 15 and 19 controls a supply or dischargeof the operating liquid to or from the cylinder unit 1, therebyresulting in control of suspension characteristics.

In addition thereto, when an ignition switch is OFF, only control iscarried out for lowering a ride height of the vehicle body for a givenperiod of time (in this embodiment, the period of time being set to twominutes) from the time when the ignition switch was turned OFF. In otherwords, in order to maintain a reference ride height of the vehicle body,control is implemented to prevent the vehicle's ride height frombecoming partially higher upon changes in load resulting from gettingout or for other reasons.

(4) Safety Valve 26

The safety valve 26 is closed by excitation at the ordinary time andopened at the fail time. For instance, the fail time may include, forexample, when a portion of the flow amount control valve 15 or 19 arefixed, when a sensor or other unit, as will be described hereinafter,gets out of order, when the liquid pressure of the operating liquidbecomes lost or insufficient, when the pump 11 gets out of order, and soon.

In this embodiment, on top of that, the safety valve 26 is opened in agiven period of time, for example, in two minutes, after the ignitionswitch was turned OFF.

It is to be noted herein that, when the safety valve 26 is opened,closure of the pilot valve 16 is delayed, as have been describedhereinabove.

(5) Pilot Valve 16

As have been described hereinabove, the pilot valve 16 is opened in adelayed manner due to the action of the orifices 32F and 32R after thepressure in the common passage 13 has been decreased. At the fail time,for example, when a portion of the flow amount control valves 15 is keptopen, this arrangement allows the passages 14FR, 14FL, 14RR and 14RL tobe closed on account of a decrease in the pilot pressure resulting fromthe opening operation of the safety valve 26 and confining the operatingliquid in the cylinder units 1FR, 1RL, 1RR and 1RL, respectively,thereby maintaining the ride height of the vehicle body. It is noted asa matter of course that suspension characteristics at this time arefixed in a so-called passive fashion.

Control System

FIG. 3 represents a control system of the operating liquid circuit asshown in FIG. 1. As shown in FIG. 3, reference symbol "WFR" stands for aright-hand front wheel, "WFL" for a left-hand front wheel, "WRR" for aright-hand rear wheel, and "WRL" for a left-hand rear wheel. A vehiclebody B is provided with various sensors, respectively, including rideheight sensors 51FR, 51FL, 51RR and 51RL which are disposed in each ofthe cylinder units 1FR, 1FL, 1RR and 1RL for sensing heights of thevehicle body in the positions of the respective wheels, pressure sensors52FR, 52FL, 52RR, and 52RL for sensing the pressures in the liquidchambers 5 of the respective cylinder units 1FR, 1FL, 1RR and 1RL (seeFIG. 1, too), vertical acceleration (G) sensors 53FR, 53FL, 53RR, and53RL for sensing a vertical acceleration, i.e., acceleration in thevertical direction or a vertical component of acceleration, a vehiclespeed sensor 61 for sensing a speed of the vehicle, a steering anglesensor 62 for sensing a steering angle of the steering wheel, and atransverse acceleration sensor 63 for sensing the transverseacceleration acting upon the vehicle body. Reference symbol "U" standsfor a control unit consisting of a microcomputer, into which signals areinputted from each of the vehicle's ride height sensors 51FR, 51FL,51RR, 51RL, the pressure sensors 52FR, 52FL, 52RR, 52RL, the verticalacceleration sensors 53FR, 53FL, 53R, and the sensors 61, 62 and 63, aswell as which generates its signal to the switch valves 9 (9FR, 9FL,9RR, 9RL), the supply flow amount control valves 15 (15FR, 15FL, 15RR,15RL), the discharge flow amount control valves 19 (19FR, 19FL, 19RR,19RL), an alarm 65, such as an alarming lamp, a buzzer or the like, andthe safety valve 26.

It is provided, however, that FIG. 3 represents two verticalacceleration sensors 53FR and 53FL disposed on the forward side of thevehicle body B as indicated by the dot-and-dash line in FIG. 3 on theaxis of the front wheels and in substantially bilaterally symmetricalpositions from the central line of the body passing through thegravitational center in the longitudinal direction thereof and onevertical acceleration sensor 53R disposed on the rearward side of thevehicle body B on the axis of the rear wheels and at a substantiallyhalfway position with respect to the central line in the longitudinaldirection of the body. The three vertical acceleration sensors are setso as to form a one virtual plane representing the vehicle body B whichis an approximately horizontal plane--in other words, so as to belocated at substantially the same height.

FIG. 4 shows another example of the disposition of three verticalacceleration sensors 53FR, 53FL, and 53R. As shown in FIG. 4, the twovertical acceleration (G) sensors 53FR and 53FL located in theright-hand and left-hand positions on the front side of the body, on theone hand, are disposed in the right-hand and left-hand end portions ofan instrument panel in the vehicle compartment, respectively. The twovertical acceleration sensors 53FR and 53FL are further located in thepositions substantially bilaterally symmetrical with respect to thecentral line of the body in its longitudinal direction. The verticalacceleration sensor 53R. on the other hand, is located in a trunk roomformed in a position rearward of the vehicle compartment and is disposedon the rear side of the body and on the substantially central line inthe longitudinal direction of the body.

Referring to FIG. 4, reference symbol "BUF" denotes a valve unit inwhich at least flow amount control valves 15FR, 15FL, 19FR and 19FL forthe front wheels are incorporated, and reference symbol "BUR" denotes avalve unit in which at least flow amount control valves 15RR, 15RL, 19RRand 19RL for the rear wheels are incorporated.

Turning now to FIG. 5, there is shown a structure of the verticalacceleration (G) sensor 53 (53FR, 53FL, and 53R). The verticalacceleration sensor 53 comprises a casing 71, a beam 72 disposed in thecasing 71, and a weight 73. The beam 72 is composed of an elasticmember, and one end of the beam 72 is fixed to the casing 71 while theweight 73 is mounted on the other end thereof, or a free end thereof. Tothe beam 72 is attached a warping gauge 74. The vertical accelerationsensor 53 having the above structure is used in such a state that thecasing 71 is fixed to the body B. This arrangement of the verticalacceleration sensor 53 allows the beam 72 to warp as shown by atwo-dot-and-dash line in FIG. 5 when acceleration in the verticaldirection acts upon the body B and an extent of the acceleration in thevertical direction is sensed by means of the warping gauge 74 as awarped amount of the beam 72, then leading the sensed value to thecontrol unit U through a lead wire 75.

Active Control

An example of control over the suspension characteristics on the basisof output of each sensor will be described with reference to FIGS. 6 to8, and this corresponds to the content of step P16 in FIG. 11.

The control content may roughly be broken down into three control modes:a first control mode of controlling the posture of the vehicle body B onthe basis of output from the vehicle's ride-height sensor, a secondcontrol mode of controlling ride comfort on the basis of output from thevertical acceleration (G) sensors, and a third control mode ofcontrolling the warping of the vehicle body B on the basis of output ofthe pressure sensor.

(1) First Control Mode (Control over Signals From Vehicle's Ride-HeightSensor)

This control mode comprises control over three components of the postureof the body, namely, a bounce component, a pitch component, and a rollcomponent of vibration, each of which may be regulated by feedbackcontrol by means of PI control.

For the control over the three components of vibration in the posture ofthe body, the way of dealing output from each of the vehicle'sride-height sensors is indicated by plus (+) or minus (-) symbols on theleft side of each of a bounce control section, a pitch control section,and a roll control section in the drawing. The symbols (+) and (-)indicated on the right side thereof represent control to be carried outby each of the control sections for regulating changes in the posture ofthe body and these symbols are opposite to those provided on the leftside of each of the control sections in the drawing.

In other words, for the control over the bounce component of the postureof the body, the PI control is carried out in such a manner that the sumof the vehicle's ride heights on its right-hand and left-hand frontwheel sides and the sum of the vehicle's ride heights on its right-handand left-hand rear wheel sides are brought into agreement with acorresponding reference ride height. For the control of the pitchcomponent of the posture of the body, the PI control is carried out insuch a manner that the difference of the sum by adding the vehicle'sride heights on the right-hand and left-hand rear wheel sides of thebody from the sum obtained by adding the vehicle's ride heights on itsright-hand and left-hand front wheel sides thereof gives zero. For thecontrol of the roll component of the posture of the body, the PI controlis implemented such that the sum of the vehicle's ride height on itsright-hand front wheel side and the vehicle's ride height on itsright-hand rear wheel side is brought into agreement with the sum of thevehicle's ride height on the left-hand front wheel side and the rideheight on the left-hand rear wheel side--in other words, such that theroll component of vibration gives a target rolling angle T_(ROLL).

The control values obtained for three of the foregoing PI control aregiven for each of the four cylinder units 1 and the control values foreach cylinder unit 1 are added and determined as four flow amountsignals Q_(XFR), Q_(XFL), Q_(XRR) and Q_(XRL) for final control over theposture of the vehicle body.

(2) Second Control Mode (Control over Signals from Vertical Acceleration(G) Sensors)

This control mode is to prevent impairment of ride comfort resultingfrom the control over the posture of the body as have been described initem (1) above. Thus, for this control, the feedback control (in thisembodiment, proportional control) is carried out so as to regulateacceleration in the vertical direction for the control over the postureof the body corresponding to three components: the bounce component, thepitch component, and the roll component of vibration, as have beendescribed in item (1) above. In this case, it is preferred to setcontrol gains K_(B3), K_(P3) and K_(R3) as values different from eachother (for example, K_(B3) >K_(R3) >K_(P3)) so as to permit anappropriate control of the bounce, pitch, and roll components ofvibration of the body.

It is noted herein that, as only three vertical acceleration (G) sensorsare provided for this second control mode, in this embodiment, there isused an arithmetic mean of the vertical acceleration on the right-handand left-hand front side of the body as acceleration in the verticaldirection on the frcnt side for the pitch control.

For the roll control mode, only the acceleration in the verticaldirection on the right-hand and left-hand front side can be used whilethe acceleration in the vertical direction on the rear side is not used.

It is to be understood that, since the rolling of the body occurs on theside of the rear wheels after on the side of the front wheels (presumingthat the front wheels are steered), it is preferred to carry out theroll control on the rear wheel side in a somewhat delayed manner afterthe control mode of the roll component on the front wheel side hasstarted. In this case, furthermore, a control gain on the side of thefront wheels may be changed from that on the side of the rear wheels insuch a manner that the control gain on the rear wheel side becomessmaller than the control gain on the front wheel side. It is alsopossible that a time delay and the control gain may be variable inaccordance with a running state such as a coefficient of friction onpavement, a steered angle, a velocity of steered angles, a vehiclevelocity and so on.

From the standpoint of the fact that rolling on the front wheel sideoccurs earlier than that on the rear wheel side, it is preferred thatthe two vertical acceleration sensors be disposed on the left-hand andright-hand front sides of the body rather than on the left-hand andright-hand rear side of the body.

In the second control mode, too, the control values are obtained foreach of the four cylinder units 1 by the above three proportionalcontrol. Then the control values for each of the cylinder units 1 arethen added and the four added values are determined eventually as flowamount signals Q_(GFR), Q_(GFL), Q_(GRR) and Q_(GRL) for the controlmodes for the respective wheels.

As have been described hereinabove, the control over the roll componentof vibration on the rear wheel side of the body is carried out in such asomewhat delayed manner after commencement of the control over the rollcomponent on the front wheel side. Thus, as shown in FIG. 6, the flowamount signals utilizing control gains L and Q can be controlled at aninitial stage of steering immediately before the flow amount signalsQ_(GFR), Q_(GFL), Q_(GRR) and Q_(GRL) are given. In other words, thecontrol gain L for the front wheels is always set to "1" even if thevehicle is running straight or cornering, while the control gain Q forthe rear wheels are set to "1" in an ordinary case and set to a valuesmaller than "1" only at an initial stage of cornering, for example, to"0.8" (decreasing the control gain) or "0" (delayed). It is furtherpossible to provide only the flow amount signals for the rear wheelsfrom the roll control section with a delay circuit D which can bearranged so as to operate at an initial stage of steering, therebyexecuting this delay, while to be suspended at the time other than theinitial stage of cornering, thereby executing no delay.

FIG. 7 shows a block diagram showing a control system for determiningthe control gains L and Q and for operation or suspension of the delaycircuit D. As shown in FIG. 8, reference numeral 62 denotes a sensor forsensing a steered angle, θ_(H), of a steering wheel (see FIG. 3), and avelocity of the steered angle, θ_(H'), is obtained by differentiatingthe steered angle θ_(H) of the steering wheel. When the velocity of theangle θ_(H'), is judged by a judgment section to be equal to or largerthan a reference value, on the one hand, the control gain L is set to"1" while the control gain Q is set to "0" (or "0.8"). Furthermore, thedelay is executed together with the settings. When the velocity of thesteered angle, θ_(H'), is judged by the judgment section to be smallerthan the reference value, α, on the other hand, the two control gains Land Q are set each to "1" and no delay is executed at this time.

(3) Third Control Mode of Controlling the Warping (Control over PressureSignals)

The third control mode is to control the warping of the vehicle body B.In other words, the pressure acting upon each of the cylinder units 1corresponds to a load applied to each of the respective wheels so thatcontrol of the warping of the body B resulting from the load is carriedout so as to make the warping unlikely to become larger.

More specifically, this control mode basically is carried out byimplementing feedback control in the direction in which a ratio of thedifference of the pressures on the sides of the right-hand and left-handfront wheels to the sum of the pressures thereof is brought intoagreement with a ratio of the difference of the pressures of theright-hand and left-hand rear wheels to the sum of the pressuresthereof. And the control ratio of an warped amount on the front side ofthe body to a warped amount on the rear side thereof is determined bycorrection using a correction coefficient ωF, and a control ratio of thecontrol over the posture of the body as have been described in the item(1) above to the control over ride comfort as described in item (2)above is given by correction with a correction coefficient ωA. In thecontrol for regulating this warping, the control values are determinedeventually as flow amount signals Q_(PFR), Q_(PFL), Q_(PRR) and Q_(PRL)for each of the four cylinder units 1.

Each of the flow rate signals for the control over the posture of thebody, for the control over ride comfort, and the control over thewarping for each of the four cylinder units 1 is eventually added toeach other and determined as final flow amount signals Q_(FR), Q_(FL),Q_(RR) and Q_(RL) and each of the flow rate control valves 15 and 19 arecontrolled so as to allow a flow amount to correspond to each of thefinal flow amount signals Q_(FR), Q_(FL), Q_(RR) and Q_(RL),respectively.

(4) The control gains for the control formulas used for the foregoingexplanation of FIG. 6 can be switched by a control system as will bedescribed as will be described with reference to FIG. 8.

The steering angle θ_(H) of the steering wheel is multiplied by thevehicle velocity V, and a value S₁ is given by subtracting a referencevalue G₁ from the product, θ_(H) ·V, and the value S₁ is input into thecornering judgment section. A value G₂ is given by subtracting areference value G₂ from the current transverse acceleration, Gs, andinputted into the cornering judgment section. When S₁ ≧0 S₂ ≧0, on theone hand, the cornering section judges that the vehicle is cornering andgenerates a signal S_(a) for changing the suspension characteristic to aharder state while setting each of control constants Ki (i=B₁, P₁, R₁,B₃, P₃, R₃) to a value K_(hard), thereby shifting the damping-forceshift valve 9 to the close position in order to improve the ability tofollow the control of the flow amount to each of the liquid pressurecylinders 3. Furthermore, there is set a value corresponding to thetransverse acceleration at that time from a map which stores the targetroll angles T_(ROLL). FIG. 9 shows one example of the map. It is notedthat the normal roll angles become larger as the transverse accelerationincreases for the vehicle with the passive suspension. When the value S₁<0 or S₂ <0, on the other hand, the cornering judgment section judgesthat the vehicle is running straight and generates a signal S_(b) forchanging the suspension characteristic to a softer state, therebyshifting the damping-force shift valve 9 to the cornering position.Further, the control coefficients Ki are set each to a usual valueK_(soft) and the target roll angle T_(ROLL) is set to 0.

Trouble Control

Whether the supply control valve 15 is fixed while it is kept open, inother words, whether the operating liquid is kept supplied to thecorresponding cylinder unit 1, is checked by the procedure whichfollows.

First, a total stroke amount of each of the rebounding and bumpingwheels is set to 80 mm and the value on the rebounding side is providedwith plus (+) symbol while the value on the bumping side is providedwith minus (-) symbol. The vehicle's ride height sensor 51 senses thebounce and bump components and output of the sensor 51 ranges from -80mm to +80 mm as the stroke amount of the wheel.

Given the foregoing, the supply control valve 15 is judged as being introuble, namely, as being fixed in an open state, when the followingfour conditions are met, in which a reference ride height of the vehicleis given as Ho when neither bump nor rebound occur, a current rideheight as H(t), the ride height immediately prior to the current rideheight as H(t-Δt), a current pressure within the cylinder unit as P(t),and the pressure within the cylinder unit immediately prior to thecurrent pressure as P(t-Δt).

Condition a: The rebound occurs, i.e.,

H(t)-Ho>0.

Condition b: The rebound further occurs from the state of Condition a,i.e.,

H(t)-H(t-Δt)>0.

Condition c: The pressure within the cylinder unit is elevating, i.e.,

P(t)-P(t-Δt)>0.

Condition d The state of Condition c continues for a given time (forexample, 300 msec).

When it is sensed that the supply control valve 15 is fixed, the alarm65 (FIG. 3) such as an alarm lamp or an alarm buzzer may be operated tomerely notify the driver. It is further preferred that fail control becarried out. The fail control may be implemented by releasing thepressure on the side of the accumulator 22 as well as by operating thealarm 65. Concurrently with the opening operation of the safety valve26, signals are given to all control valves 15 and 19 for full open fora given period of time, for example, for one second. Further, the pilotvalve 16 is maintained in an open state for a given period of time (forapproximately one second) by means of the delay action of the orifice 32as have been described hereinabove. During that period of time, theoperating liquid in the cylinder 2 is discharged through the supplycontrol valve 15 or the discharge control valve 19, thereby the rideheight of the body is lowered to its lowest position, in other words,down to a bump stopper. Thereafter, the pilot valve 16 is closed withinshort so that the ride height of the body is maintained in its lowestposition.

At the fail time, the active control cannot be done in a good fashion.Thus, it may be arranged such that the active control itself cannot beexecuted and it cannot be returned until it is repaired, for example, bystoring the fail time in an unvolatile memory and turning the ignitionon again after once the ignition was turned off. As a matter of course,if one of the supply control valves 15 is judged to be in trouble, thefail control is carried out in the manner as have been describedhereinabove.

In this example, the trouble can be sensed when the discharge controlvalve 19 is fixed in an open state. In this case, to the contrary incase of the flow amount control valve 15, attention is paid to the pointthat the pressure in the cylinder unit 1 should be elevated when thewheel is bumped. Thus, the discharge control valve 19 is judged to be introuble when the following four conditions are met.

Condition e: The bump occurs, i.e.,

H(t)-Ho<0.

Condition f: The bump further occurs from the state of Condition e,i.e.,

H(t)-H(t-Δt)<0.

Condition g: The pressure within the cylinder unit is lowering, i.e.,

P(t)-P(t-Δt)<0.

Condition h: The state of Condition g continues for a given time (forexample, 300 msec).

When it is judged that the discharge control valve 19 is in trouble, thecontrol can be made by prohibiting the active control from beingreturned until it is repaired, in the same manner as in the fail controllike the supply control valve 15.

Flow Charts (FIGS. 11 & 12)

The trouble control for the supply control valve 15 and the dischargecontrol valve 19 will be described with reference to the flow chart asshown in FIG. 11.

First, the system is started by turning the ignition switch on. At stepP1, whether flag A or B is "1" or not is judged. The flag A is set to"1" when it is judged that the supply control valve 15 is in troublewhile the flag B is set to "1" when the discharge control valve 19 isjudged to be in trouble. They are stored in an unvolatile memory.

When it is judged at step P1 that the flag A or B is set to "1", on theone hand, the control concludes to prohibit the active control. When itis judged that neither flag A nor flag B are set to "1", the system isinitialized at step P2 and the control valve 26 is closed at this time.

Then the flow proceeds to step P3 where all data are input and allsignals from the sensors are read. At steps P4 to P7, the troublecontrol is implemented for the supply control valve 15, in other words,it is judged whether the foregoing conditions to d are met or not. IfYES at all the steps P4 to P7 (when it is judged that all the conditionsa to d are met), then the flow advances to step P8 and flag A is set to"1". Thereafter, at step P9, the fail control is carried out and thecontrol ends in the same state.

When it is judged NO at all steps P4 to P7, in other words, when eitherof the conditions a to d is not met, the flow proceeds to step P10 whereit is judged whether or not the condition e above is met. When YES atstep P10, the flow goes to step P11 where it is judged whether or notthe condition f above is satisfied. After it is judged at step P11 thatthe condition f is met, whether the condition is met or not is thenjudged at step P12. When YES at step P12, then the flow goes to step P13where it is judged whether or not the condition h is satisfied. When itis judged at step P13 that the condition h also is met, then flag B isset to "1" at step P14 and the fail control is executed at step P15. Thecontrol then concludes.

On the contrary, when it is judged at steps P10 to P13 that either ofthe conditions e to h is not met, the flow advances to step P16 wherethe active control is carried out in the manner as shown in FIGS. 6 to8.

FIG. 12 shows the flow chart for the fail control as shown at steps P9and P15 in FIG. 11. At step P21, the alarm 65 is operated to notify thedrive of the fail time. Then the safety valve 26 is opened at step P22and each of the control valves 15 and 19 are full open at step 23. Whenthe signals for full opening are outputted, then the ride height islowered.

Then at step P24, it is judged whether or not a given period of time inthis example, one second--has elapsed after the process at step P23. IfNO at step P24, the flow is returned to step P24, on the one hand, andthe full open states of the control valves 15 and 19 are maintained.When the given period of time has elapsed, on the other, the flowproceeds to step P25 where the control valves 15 and 19 are brought to afull open state. Signals for closing all the control valves 15 and 19are generated to them, and then the control ends.

Although the foregoing description is directed to the embodiment wherethe supply control valve 15 is disposed separately and independentlyfrom the discharge control valve 19, the supply control valve 15 and thedischarge control valve 19 may be constructed using one electromagneticvalve having three ports and three positions.

It is to be understood that the foregoing text and drawings relate toembodiments of the invention given by way of examples but notlimitation. Various other embodiments and variants are possible withinthe spirit and scope of the present invention.

What is claimed is:
 1. A suspension apparatus of a vehicle, comprising:acylinder unit interposed between a sprung weight and an unsprung weightfor changing a ride height by supplying or discharging an operatingliquid; a supply/discharge control valve for supplying to or dischargingfrom the cylinder unit; a supply/discharge control means for controllingsupply of the operating liquid to or discharge of the operating liquidfrom the cylinder unit by controlling the supply/discharge control valveon the basis of a predetermined condition; a rebound detecting means fordetecting a rebound of a wheel and for detecting further rebounding ofthe wheel after an initial rebound of the wheel is detected; a pressuredetecting means for detecting a pressure in the cylinder unit; and atrouble detecting means for detecting that the supply/discharge controlvalve is operating outside of predetermined normal values when thepressure detected by the pressure detecting means continues in aelevated state for a given period of time when the rebound is detectedby the rebound detecting means.
 2. A suspension apparatus as claimed inclaim 1, wherein a gas spring is connected to the cylinder unit.
 3. Asuspension apparatus as claimed in claim 2, wherein a plurality of thegas springs are connected in parallel to each other to one cylinderunit.
 4. A suspension apparatus as claimed in claim 3, wherein anorifice is interposed between the cylinder unit and each of the gassprings.
 5. A suspension apparatus as claimed in claim 4, wherein avariable orifice is interposed between the cylinder unit and a portionof the gas springs, the variable orifice being controlled so as to makean effective opening area smaller during cornering than during straightdriving.
 6. A suspension apparatus as claimed in claim 2, wherein anorifice is interposed between the cylinder unit and the gas spring.
 7. Asuspension apparatus as claimed in claim 6, wherein a variable orificeis interposed between the cylinder unit and the gas spring so as to becontrollable on the basis of a predetermined condition.
 8. A suspensionapparatus as claimed in claim 1, further comprising:a reservoir tank forstoring the operating liquid; a supply passage connecting the reservoirtank to a supply control valve of the supply/discharge control valve; arelief passage connecting the reservoir tank to a discharge controlvalve of the supply/discharge control valve; a pump connected to thesupply passage for pumping up the operating liquid from the reservoirtank and supplying the operating liquid to the supply passage; and amain accumulator connected to the supply passage for storing theoperating liquid of a high pressure pumped up by the pump.
 9. Asuspension apparatus as claimed in claim 8, wherein a bypass bypassingthe discharge control valve and communicating the cylinder unit with thereservoir tank; anda relief valve is connected to the bypass, the reliefvalve being arranged so as to be opened when the pressure in thecylinder unit reaches a given value or higher.
 10. A suspensionapparatus as claimed in claim 8, further comprising a safety valve forreleasing a pressure in the main accumulator to the reservoir tank. 11.A suspension apparatus as claimed in claim 10, wherein the safety valveis connected to the relief passage.
 12. A suspension apparatus asclaimed in claim 11, wherein a sub-accumulator is connected to therelief passage.
 13. A suspension apparatus as claimed in claim 11,wherein there is provided with a trouble control means for opening thesafety valve when the trouble detecting means detects that thesupply/discharge control valve is operating outside of saidpredetermined normal values.
 14. A suspension apparatus as claimed inclaim 13, wherein the trouble control means is controlled so as to openall supply/discharge control valves.
 15. A suspension apparatus asclaimed in claim 14, wherein the trouble control means is controlled soas to open all the supply/discharge control valves for a given period oftime and to close all of them after elapse of the given period of time.16. A suspension apparatus as claimed in claim 8, wherein a blockingmeans is interposed between the supply control valve and the cylinderunit for blocking a communication of the supply control valve with thecylinder unit by delaying from reduction in a pressure of the mainaccumulator when the pressure of the main accumulator is reduced.
 17. Asuspension apparatus as claimed in claim 16, wherein the blocking meanscomprises a pilot valve and an orifice;the pilot valve being interposedbetween the supply control valve and the cylinder unit for operatingopening or closing the blocking means using a pressure of the mainaccumulator as a pilot pressure; and the orifice being connected to apilot passage leading the pilot pressure to the pilot valve.
 18. Asuspension apparatus as claimed in claim 8, further comprising:a safetyvalve for releasing a pressure in the accumulator to the reservoir tank;a blocking means interposed between the supply control valve and thecylinder unit for blocking communication of the supply control valvewith the cylinder unit by delaying reduction in pressure of the mainaccumulator when the pressure of the main accumulator is reduced; atrouble control means for opening the safety valve and for opening allof the supply/discharge valves when the trouble detecting means detectsthat the supply/discharge control valve is operating outside of saidpredetermined normal values.
 19. A suspension apparatus as claimed inclaim 18, wherein the trouble control means is controlled so as to openall the supply/discharge control valves for a given period of time andto close all of them after elapse of the given period of time.
 20. Asuspension apparatus as claimed in claim 1, wherein the rebounddetecting means comprises a ride height detecting means for detecting aride height of a vehicle body, or a stroke position of the wheel withrespect to the vehicle body.
 21. A suspension apparatus as claimed inclaim 1, further comprising a ride height detecting means for detectinga ride height of a vehicle body, or a stroke position of the wheel withrespect to the vehicle body;wherein the supply/discharge control meanscontrols the supply/discharge control valve in such a manner that amode-corresponding posture corresponding to each of three modes of aposture of the vehicle, three modes being a bounce mode, a pitch modeand a roll mode, obtainable on the basis of output from the ride heightdetecting means is located so as to comply with a predeterminedcondition.
 22. A suspension apparatus as claimed in claim 21, furthercomprising an acceleration sensor for detecting a vertical accelerationof the vehicle body;wherein the supply/discharge control means controlsthe supply/discharge control valve so as to regulate the verticalacceleration of the vehicle body detected by the acceleration sensor.23. A suspension apparatus as claimed in claim 22, wherein:at leastthree acceleration sensors are mounted so as to detect the verticalacceleration corresponding to each of the three modes; and thesupply/discharge control means controls the supply/discharge controlvalve so as to regulate the vertical acceleration corresponding to thethree modes, obtainable on the basis of at least the three accelerationsensors.
 24. A suspension apparatus as claimed in claim 1, wherein:thesupply/discharge control means is a flow amount control valve; and acontrol value of the supply/discharge control means is determined as aflow amount signal.
 25. A suspension apparatus as claimed in claim 24,wherein the supply/discharge control valve is provided with apressure-differential adjusting function of adjusting a pressuredifferential between a pressure on an upstream side and a pressure on adownstream side to a constant value.
 26. A suspension apparatus asclaimed in claim 24, further comprising:a ride height detecting meansfor detecting a ride height of a vehicle body, or a stroke position ofthe wheel with respect to the vehicle body; and an acceleration sensorfor detecting a vertical acceleration of the vehicle body; wherein thesupply/discharge control means comprises a first control means, a secondcontrol means and a third control means; wherein the first control meansdetermines a control value for the supply/discharge control valve so asto control the supply/discharge control valve in such a manner that amode-corresponding posture corresponding to each of three modes of aposture of the vehicle, three modes being a bounce mode, a pitch modeand a roll mode, obtainable on the basis of output from the ride heightdetecting means is located so as to comply with a predeterminedcondition; the second control means determines a control value for thesupply/discharge control valve so as to regulate the verticalacceleration of the vehicle body detected by the acceleration sensor;and the third control means determines a control value for thesupply/discharge control valve so as to regulate a warp between a frontportion and a rear portion of the vehicle body obtained on the basis ofoutput from the pressure detecting means.
 27. A suspension apparatus asclaimed in claim 26, wherein the sum of the control values determined bythe first, second and third control means is determined as a finalcontrol value for the supply/discharge control means.
 28. A suspensionapparatus as claimed in any one of claims 8 to 27, wherein a gas springis connected to the cylinder unit.
 29. A suspension apparatus as claimedin claim 28, wherein an orifice is interposed between the cylinder unitand the gas spring.
 30. A suspension apparatus as claimed in any one ofclaims 1 to 27, further comprising an alarm operable when troubledetecting means detects that the supply/discharge control valve isoperating outside of said predetermined normal values.